Seedling container

ABSTRACT

Peat and water are mixed to form a thick paste which is extruded into a plastic film casing. The casing and filling are sliced into short, open-ended units. The units provide containers in which seedlings can be grown. When the seedlings are to be planted, the casing is perforated or shredded with a knife and the peat plug and seedling root ball buried together.

United States Patent Creighton et a1.

SEEDLING CONTAINER Inventors: Stephen Mark Creighton; David LawrenceMitchell; William Chee Kay, all of Edmonton, Alberta, Canada ResearchCouncil of Alberta, Edmondson, Alberta, Canada Filed: July 19, 1971Appl. No.: 163,810

Assignee:

US. Cl 47/56, 47/37 Int. Cl. A0lc 1/04 Field of Search 47/37, 56

References Cited UNITED STATES PATENTS 5/1934 Otwell 47/37 3/1957Clawson 47/37 X [451 Jan. 29, 1974 3,172,234 3/1965 Eavis 47/56 X3,362,106 l/l968 Goldring... 3,456,386 7/1969 Holden 47/56 FOREIGNPATENTS OR APPLICATIONS 760,162 6/1967 Canada 47/34.13

2 Claims, 7 Drawing Figures PATENTEDJMI 29 I974 PEAT sum 1 or 5SCREENING MIXING WATER EQUILIBRATION sfraalooa PATENTED JAN 2 9 i974 sum2 or PATENIEI] JAN 2 9 I974 sum u or 6 ajmsgow 0 1 SEEDLING CONTAINERBACKGROUND OF THE INVENTION This invention pertains to a peat plug, to aseedling container unit incorporating the plug, and to a method formanufacturing the seedling container units. Application is found for thecontainer units in the propagation of tree seedlings for reforestationprojects, and in other areas of horticulture.

For many decades, seedling stock for reforestation has largely beenprovided using the bare root method. This involves planting seeds inoutdoor seed beds and rearing the seedlings there for two or threeyears. When properly matured, the seedlings are lifted; this is usuallydone in the late fall when the plants are dormant. The bare rootseedlings are then usually held in cold storage until spring, when theyare outplanted in the forest.

This technique has several disadvantages. For example, the rearingperiod is long and therefore expensive. A substantial number of theplants die while in the seed beds or when their roots are exposed to airduring the lifting and storing operations. In addition, the plantingseason is very short and the whole process is labor intensive.

Over the past decade, nursery practice has changed and in many casesseedlings are now grown in small individual container units undercontrolled conditions in a greenhouse or in a hothouse in milderclimates. After 8 to 20 weeks of growth, the seedlings are taken to theforest and outplanted.

One important advantage of this latter practice is that it lends itselfto mechanization, with attendant savings in labor and time. Since manymillions of these seedlings must be planted in North America each year,any improvement along this line is useful. In addition, the time factorinvolved in raising the seedlings is greatly reduced. The seedlings aregrown under ideal conditions, and they are planted withtheir rootingmedium attached to provide a water-absorptive and retentive reservoir.

The prior art container units consist of two parts: the outer container,and the rooting medium, usually peat, with which it is filled. One suchouter container comprises a styrofoam plastic block having a number ofspaced cavities formed therein. The block has the appearance of asingle-layer honeycomb. Each cavity has a depth of about 4 7a inches anda diameter of 1 inch; it is filled with 2 3 cubic inches of loose, dry,handpacked peat. An opening is provided at the base of each cavity toallow for the drainage of excess water. Another known containercomprises a cylinder of stiff paper or plastic which is slitlongitudinally and handpacked with peat. In this latter case, thecontainers are separate; in the former case, they are joined together toform the block. In both cases, the outer container functions, at thegreenhouse stage, to retain moisture and prevent intertwining of theroot systems of adjacent plants. The container is left on while theseedlings are transported to the field and serves to hold the root ballsintact. In the case of the block, the seedling and root ball areextracted together from the container and planted. In the case of thetubeling, the container is left in place around the root ball when it isplanted.

It will be noted that the rooting medium commonly used in seedlingcontainer units is peat; since the present invention is partly concernedwith controlling the properties of peat, it is useful at this point todescribe the material in some detail.

Peat is a soil containing at least 50 percent by weight organic matter.The organic material is the decomposition product of various types ofplants. Peat originating from sphagnum moss has long been preferred forhorticultural purposes because of its exceptional waterabsorptive andretentive properties.

Peats are classified according to their state of decomposition. Arelatively undecomposed peat is comprised of the intact skeletons ofleaves and stems. This material is fibrous in form and, in theaggregate, provides a loose, porous structure. On the other hand, peatin an advanced state of decomposition is amorphous and colloidal instructure. The former is capable of absorbing and holding large amountsof water while the latter is not. The Von Post scale is commonly used inthe art to indicate the state of decomposition it runs from I to 10.Most peats used for horticultural purposes have a Von Post rank of l or2.

Table 1 illustrates the differences in water-absorbing capacity andparticle size which are present in two peats at different stages ofdecomposition:

TABLE I Von absorptive Fibre Size (mm) Post value/I00 grams rank drypeat 2.0 2 l .l sphagnum I 1935 57.4 22 3 20.3 sphagnum 5 373 5.7 35.858.5

Peats normally contain soluble ionic salts, such as alkali metal salts.Since these salts are usually harmful to plant growth, it is prudent tochoose peat having a low extractive salt content for seedlingcontainers.

Peat is characterized by porosity and permeability. In other words, ithas void spaces which are capable of holding water, and many of thesevoids are interconnected so that moisture can readily move through themass. The capacity and rates of hydration and dehydration of the peatwith reference to water are therefore affected by its porosity andpermeability.

The voids or pores within the material vary in size; this sizedistribution is of significance to the suitability of the peat as arooting medium in the field. More particularly, the largest proportionof the water held by peat is located in relatively large pores and istermed drainage water. This water is free to move out of the peat intothe surrounding soil should the soil be dry. It is conventional todescribe the drainage water as that water which can be displaced frompeat by pressures of 1/10 to H3 bar (i.e., 1.5 5 p.s.i.). A secondportion of the water held by peat is termed capillary-bound water. Thisis water which cannot move into the surrounding soil but is available tobe taken up by the plant. Capillary-bound water is conventionallydescribed as the water which can be displaced from peat by pressures ofl/3 bar to 15 bar (i.e., 5 p.s.i. to 225 p.s.i.). The remaining waterwithin peat is termed hygroscopic water. It is retained in the tiniestcapillaries with a tension greater than the osmotic pressure which canbe exerted by the root system.

The water capacity of peat and the state of the capillaries aredeleteriously affected by the processing to which the material isusually subjected. Since peat is usually wet in its natural state, it isconventional to kiln dry it to about 40 percent retained moisture.Kilndrying irreversibly collapses a number of the capillaries and thusreduces the volume of water which the peat can hold in thecapillary-bound condition.

In the course of the work on this invention, we have come to recognizethat several features are desirable in the peat plug used in a plantcontainer. It should, of course, contribute toward achieving areasonable rate of growth of the seedling in the greenhouse. In thisconnection, the plug should be of ample size and capable of providing asuitable reservoir of water and water soluble nutrients, to the plant.The peat should be sufficiently loose so that the plant roots canreadily extend through it. When outplanted, the plug should function asa reservoir and also have particular characteristics which aid the plantto survive. In this connection, the plug should be capable of rapidhydration and slow dehydration so that it will accumulate moisture fromthe soil when it is available but will conserve its own water when thesoil is dry. It should also have a relatively large capillary-boundwater capacity; this retained water helps to tide the plant over duringperiods of drought. Since the plug must be handled during planting, itshould have enough mechanical strength to hold together during thisoperation.

The outer container should also have several attributes. Firstly, itshould incorporate an air-pruning opening to encourage the developmentof a thick system of roots during the greenhouse stage. It is known thatroots wilt on contacting air; this fact is used to advantage incontainer practice by providing an airpruning opening at the base of thecontainer. when one root emerges through the opening and is pruned,another sprouts; in this manner, a thick growth of roots is developed.Secondly, the container should be removable or destructable at the timeof planting. This permits maximum egress of the roots from the plug andprovides the opportunity for the development of a system of rootsextending both laterally and vertically into the soil. Secure anchoringis thereby achieved with the result that the plant can resist frostheaving. Also, the supply of nutrients to the plant is maximized duringthe critical period of field establishment. Thirdly, if the outercontainer is to be partially left on, it should be adapted to conform tothe contours of the hole in which it is planted. The resulting frictionfit is helpful in resisting frost heaving.

Turning now to the process of manufacture, it should be highlymechanized and automated. It would also be useful if the processconditions could be easily manipulated to control certaincharacteristics of the plug, such as the rates of hydration anddehydration and the capillary-bound water capacity. With such a process,the plug could be tailored" to the particular soil conditions in whichit is to be planted to improve plant survivability. Finally, it isdesirable that the process use non-processed peat as feed; this wouldeliminate the destruction of capillary-bound water capacity which occursduring kiln drying.

SUMMARY OF THE INVENTION It is therefore a general object of theinvention to provide a peat plug which is adapted to give adequateperformance, not only in the greenhouse, but also in the field.

It is another object to provide a peat plug having certain propertiesbuilt-in or enlarged by manufacturing procedures to improvesurvivability of the seedling in the field.

It is another object to provide a mechanically strong peat plug havingan improved rate of dehydration and an increased capillary-bound watercapacity when compared with hand-packed peat plugs.

It is another object to provide a container unit having an impermeableouter container or casing which is easily removable or destructable atthe time of planting.

It is another object to provide a unit whose outer container has a largeair-pruning opening at its base.

It is another general object to provide a process for manufacturingseedling container units and plugs which is well suited to mechanizationand automation, and which is controllable to produce units havingpredetermined properties.

It is another object to provide such a process wherein peat is therooting medium, and the process conditions can be easily varied tocontrol the properties of the plug-more particularly, the rates ofhydration and dehydration and the capillary-bound water capacity.

It is another object to provide a process of this type which can usenon-processed bog peat as feed.

In accordance with this invention, a rooting medium plug is providedwhich is adapted to promote desirable plant growth and survival both inthe greenhouse and field stages. This is accomplished by controllablyvarying the size and spacing of the rooting medium particles duringprocessing of the loose'material into plugs. Preferably, the rootingmaterial is entirely peat or its major component is peat. The medium ismixed with water to form a paste-like material which is continuouslycompressed and forced through a die into plug form; variation of thewater content is utilized as the chief means for controlling the extentof compaction and comminution. The extruded product is simultaneouslyencased in a thin, flexible, tubular casing of cylindrical or otherform. Preferably the casing is made of plastic film. This casingfunctions as a root and moisture barrier in the greenhouse but it iseasily removed or rendered inoperative, as by slitting, puncturing orperforating, at the time of planting. The encased product is divided, asby slicing it transversly, to provide seedling container units.

The development is characterized by several advantages, some of whichare as follows:

I. The process is adapted to controllably vary the density of the peatin a simple manner. This variation is reflected in changes in particlesize and spacing. Provided that these changes .are kept within certainlimits (expressed in terms of density), the changes have a beneficialeffect on the rates of hydration and dehydration of the peat. Inaddition, more peat is packed into a unit volume than would be the case,for example, with hand-packed peat. The total moisture content and thecapillary-bound water capacity of the plug are thereby additionallyincreased, with an attendant improvement in the amount of moistureavailable to the plant during dry periods. An optimized plug product,tailored to meet the soil and climate conditions of the field area inwhich it is to be planted, is thereby produced by means of adjustment ofthe plug density.

2. The improved plug is combined with an outer casing which is partiallyor completely removable. When outplanted, the bared plug's side andbottom surfaces are in direct contact with the soil. Good moisturetransmittal to the plug, the development of a lateral root system fromthe plug into the soil, and fitting together of duction rates.

BRIEF DESCRIPTION OF THE DRAWING In the drawings:

FIG. 1 is a block diagram showing the steps of the process;

FIG. 2 is a sectional side view of an extruder apparatus which is usedin the process;

FIG. 3 is a graph in which the moisture content of the feed is plottedagainst the density of the plug product;

FIG. 4 is a graph in which the effect of density of the plug on itsrehydration rate is shown by plotting moisture content of the plugagainst time;

FIG. 5 is a graph in which the effect of outer container removal onrehydration rate is shown by plotting moisture content of plugs againsttime;

FIG. 6 is a graph in which the effects on dehydration of extrusion anddensity variation are shown by plotting moisture content of plugsagainst time.

FIG. 7 is a perspective view of the container product.

DESCRIPTION OF THE PREFERRED EMBODIMENT Rooting Medium The containerplug is formed of an extrudable, waterabsorptive and retentive materialin which plant roots will grow. Preferably, this material comprises peator a mixture in which peat is the major component. Examples of thelatter are bark-peat and vermiculite-sandpeat. However the scope of theinvention is also intended to extend to artifical rooting mediums, suchas porous and permeable plastic foams.

One suitable peat is produced at Moss Spur, Manitoba, and is sold byWestern Moss Ltd. It has the following properties:

Von Post rank 1 nitrogen 0.90

% moisture 41 ash 5.4

soluble ionic salts 13S micromhos/cm. at 25 C water absorptive value 730gms. H OIIOO gms. dry

peat

1/10 bar moisture- 387 gms. I-IZOIIOO gms. dry peat /3 bar moisture-244gms. H2O/l0O gms. dry peat 15 bar moisture-130 gms. H 0/100 gms. drypeat Fluid eontent o f' ihe page The addition of water or an equivalentagent to the rooting medium prior to extrusion provides one suitablemeans for controlling the density (dry weight/wet volume) of the plugproduct. The water functions as a diluent and lubricant. It fills someof the voids within the peat and thus limits the extent to which thesevoids are closed during the compression stage of the process. Itslubricating quality aids the peat particles to move past each otherduring compression with the result that the large voids are partiallyfilled in with fine particles. Additionally, the use of water allows thepeat to move through the extruder parts with reduced friction andcomminution.

When using extrusion apparatus, such as that described below, the wateraddition to the peat must vary between about 70 and 85 percent of theweight of the mixture. If the paste fed to the extrusion operationcondense to support any reasonable degree of seedling growth and it isvery difficult to process the peat as it tends to block the extruder.This is probably due to excessive attrition of the peat. If more than 85percent water is used, the paste is too fluid for extrusion. There isconsiderable drainage, with the result that water backs up into the feedsection of the apparatus making the operation very difficult. Inaddition, the product plug is weak and tends to slump.

We prefer to use a water addition of 70 85 percent. At this consistency,the paste is adapted to extrude easily when a compression ratio of 2:1or 3:1 is used; yet the range of density of the end product issufficiently broad to cover most of the desirable specifications. Therange of 70 85 percent water addition leads to the production of plugshaving dry weight/wet volume densities between about 0.25 and 0.13.

Screening The peat is passed through a 1/2 inch screen to remove rocks,twigs and the like. 7 Mixing The peat is then mixed with water to form aviscous, paste-like mass. To illustrate this step, the materials aremixed for 35 minutes in a model 2030 Marion mixer operating at rpm.After mixing in this manner, the paste is allowed to equilibrate forabout 30 minutes and is then extruded.

Extrusion and division Following equilibration, the mass of paste issubjected to an extrusion operation wherein it is compressed and forcedthrough a die into a thin-walled, tubular plastic casing.

In FIG. 2, an extrusion apparatus is shown which is suitable forpracticing this invention. The extruder screw 1 is driven by a shaft 2coupled to the drive shaft 3a of a 3 horse power motor 3 having anoutput speed range of 90 900 r.p.m. The extruder housing 4 is taperedand has a rifled internal surface coated with chromium. The lead of thescrew flights is varied from the feed throat 8 to the head 5 to providea compression ratio of 2:1. A demountable extrusion nozzle 6 (8 X 1inches 0D.) is fitted to the head 5. The nozzle and head are coatedinternally with a low friction film, such as Teflon (trade mark). Ahopper 7 feeds paste into the extruder feed throat 8.

A foot long, 1 mil thick, 1 inch O.D. polythene casing 9 is threadedonto the nozzle 6. As the plug is extruded, it fills the casing 9 andforms a long container. The operator helps feed paste to the screw 1with one hand and holds a slight tension on the casing 9 with his otherhand. The long container is sliced with a gang cutter (not shown) intoshort lengths which are packed in trays or the like.

60 The product With reference to FIG. 7, the product is a cylindricalcontainer unit comprising an inner body or plug 1 l and outer casing 12.Usually the product is about 1 inch in diameter and has a length ofabout 3 inches. The plug is a coherent mass having sufficient mechanicalstrength to remain intact during normal handling. It is uniformly denseand has a density between 0.13 and 0.25. gm/cc It is characterized byimproved rates of hytains less than percent water, the plug product istoo dration and dehydration and capillary-bound water content whencompared with the hand-packed plugs of the prior art. Preferably, theplug is formed of peat and it is free of agents, such as cellulose orbinders, which might be deleterious to plant growth (these materialstend to promote the production of unwanted bacteria). The plastic casing12 is thin, flexible, impermeable to water and cylindrical in form. Itprovides a relatively large air-pruning opening 13 at its base. Thecasing is easily removable since it can be slit end to end and peeledoff. Alternatively, the casing is destructable in the sense that it canbe perforated to provide for lateral egress of the roots. When left on,its flexibility permits a good friction fit with the sides of the holein which the container unit is planted.

The invention and its advantages will be more clearly understood by thefollowing examples:

The invention and its advantages will be more clearly understood by thefollowing examples:

EXAMPLE I To illustrate the role played by water content in controllingthe density of the product plug, a number of runs, using the equipmentdescribed above and the conditions of Example VIII, were carried outusing peat and varying amounts of water. Table 11 sets out the pertinentdata:

TABLE II Run. Drive Extrusion Density of plug No. %H20 Speed rate (drywt./

(rpm) (fL/min) wet vol.) 74.3 400 19.1 .245 l 79.5 450 25.3 .212 1182.07 740 40.0 .182 25 84.18 250 12.6 .165

FIG. 3 illustrates the linear relationship which exists between plugdensity and variation of water content in the feed.

EXAMPLE II This example illustrates the proposition that a plug formedof extruded peat rehydrates faster than one formed of non-extruded peat.

A series of containers, having the following specifications wereprepared from Moss Spur peat:

TABLE III Plug Process of Density (dry Size and No. Manufacture wt./wetvol.) type casing Series hand-packed with .09 l" O.D., rigid lnon-extruded peat plastic tube Series hand-packed with .10 l" O.D.,rigid 2 extruded peat plastic tube Series extruded into .16 l" O.D.,plastic 3 film casing film casing Series extruded into .19 l" O.D.,plastic film casing film casing Series extruded into .22 1" O.D.,plastic 5 film casing film casing The containers were air-dried to 5percent moisture and placed on a water-saturated sand horizon. As shownin FIG. 4, the non-extruded, hand-packed plugs of Series 1 requiredabout 12 hours to reach 50 percent moisture content whereas theextruded, hand-packed plugs of Series 2 took about 6 hours to achievethe same result.

As further shown in FIG. 4, the extruded, dense plugs of Series 3, 4 and5 only required about 2 hours each to rehydrate to the 50 percent level.The variations in EXAMPLE III This example illustrates the improvementto be gained in rehydration rate when the container casing is removed.

Two extruded containers were prepared, each having a density of 0.15 anddried to 15 bar moisture content. The casing was left on one plug and itwas placed on a moist sand horizon so that moisture could only beabsorbed through the bottom cross-sectional opening. The casing wasremoved from a second plug and it was buried in a saturated sand horizonso that moisture could be absorbed through the sides and bottomsurfaces. FIG. 5 shows the rate of rehydration of the two plugs; thebared plug reached a moisture content of 80 percent within an hourwhereas the other plug required 2 hours to reach 65 percent moisture andnever passed above the percent level.

EXAMPLE IV This example illustrates the improvement obtained indehydration rate when the plug is extruded.

A series of 1 X 3 inches plugs were prepared as follows:

TABLE IV Plug No. Process Density Series 8 hand-packed, non extruded .10Series 9 hand-packed, extruded .10 Series 10 extruded .156 Series 1 Idouble extruded .185

The plugs were each saturated with water and then allowed to dry in air.A clear trend showing retardation in dehydration rate with increasingdensity was observed when the results were plotted to give FIG. 6.

EXAMPLE V A number of lodgepole pine seedlings were raised undercontrolled greenhouse conditions in containers having both extruded andnon-extruded plugs of different densities. The following growth data wasobtained:

TABLE V Seedling dry weight (milli grams) Plug After After After Density8 weeks 10 weeks 12 weeks Series .095 (non- 12 extruded 57.0 80.7 114.6Series .110 (non- 13 extruded) 74.1 87.7 99.8 Series .156 (ex- 45.6 84.4109.1

14 truded) Series .185 (ex- 41.5 64.9 68.9

15 truded) Series .224 (ex- 35.5 42.6 52.9

16 truded) From this data, it is seen that the extruded plug of lowdensity (0.156) provided as good growth as the handpacked plugs. Theseedlings in the dense (0.185 and 0.224) plugs were not able to grow asquickly as their counterparts in the porous plugs; however a reasonablerate of steady growth was still obtained.

EXAMPLE V1 1 This example illustrates the seedlings planted in extrudedplugs generally have better growth under droughting conditions than doseedlings planted in containers hand-packed with loose-fill medium.Lodgepole pine seedlings were grown in the two container types asdescribed in Example V. At week 12, the seedlings grown in theloose-fill plastic tubes were transplanted directly into a 6 inchesthick soil horizon with the tube intact; the seedlings grown in theextruded containers had the plastic wall covering stripped off prior toplanting. The five treatments were planted in blocks of four seedlingsper flat at 4 inches spacings. Twelve replicate flats were set up in thegreenhouse and their orientation and position in the greenhouse wasrandomized to minimize variation in the greenhouse. The soil horizon wassaturated with water for two days, then the watering re- ;gime wascompletely withdrawn for 10 weeks in order to simulate droughtingconditions. Seedlings were examined on alternate days and the daywilting commenced was recorded. Wilting was a qualitative subjectiveassessment of the seedling condition which 55111- ated the change inneedle color, lustre, droop, and stiffness. When 50 percent of atreatment had wilted, the

number of days from the beginning of drought was recorded. After 10weeks of drought, the soil was saturated with water for several days andthe final mortality assessed. The blocks were washed out and theseedling weight increases and percentage weight increases from week 12were recorded for both the surviving and the dead seedlings.

cantly larger in favor of the extruded containers of lowest densities.It was concluded that growth continued for a longer period of time inthe case of the extruded containers 14F and 15F and the onset ofmortality was significantly postponed. This interpretation is inaccordance with the peat moisture relationships derived above forcompressed extruded cylinders.

EXAMPLE VII This example illustrates the improved survivability andresistance to frost heaving of seedlings field planted in extruded plugswhen compared with seedlings field planted in hand-packed tubes. Twotypes of containers were tested: (a) 1 inch X 3 inches extrudedcontainers of the type produced in Example VIII and (b) %X 3 inchesrigid wall tubes hand-packed with loose-fill peat. Both types wereseeded to lodgepole pine, white spruce, and Douglas fir. They were fieldplanted when the seedlings were approximately weeks old, in a cut-oversite, known for its serious frost heaving characteristics that had beenprepared by scarifying. In this trial, the plastic skins of the extrudedcontainers (a) were perforated in many places prior to planting. Therigid wall tube was planted with and without the tube intact. Thetubelings were evaluated for survival, growth andwere 566% as fibs t heaved if the container or TABLE VI (Container type and seedling growthduring drought) Series 12 13 14F 15F 161 Container type Hand HandExtruded E.P. E. P.

' packed packed plug (E.P.)

tube tube Comparison Density (0.095) (0.1 10) (0.156) (0.185) (0.224)t-statistic Absolute increase ei gv 115.2 106.9 103.6 153.8 124.8 r14,053,115. seedlings rm 15,157, n.s. [U3 "M014, n.s. I 5 )1.76, 11.5.Percent wt. increasesurviving seed- 100 107 128 210 162 r 077, n.s.lings. 15p) 1 .86

I 052, n.s. 5 2.03 Absolute wt. increase (mg)dead seed- 32.4 71.4 95.899.1 55.0 t 5.04*** lings. (12 15p) r ,1.75" r ,,,2.31** Percent wt.increasedead seedlings..... 28 71 1 18 135 71 r 4.52*** lug 4.43

' Droughting period for seedlings planted in soil horizon: Weeks 12-22(Day 72 of drought).

ic skin was removed and stock planted as an extruded plug plus seedling.

2 Series 14F, 15F, 16F: P denotes plast t-Statistics tested forcomparison of means at the following levels of pro bability: n.s.-nosignificant difference;

* 90% probability; 95% probability; 99+% probability.

Table VI describes the growth of both the surviving seedlings and thedead seedlings when tested in the two container types; (a) rootingmedium hand-packed into a plastic tube, and (b) the compressed peatextruded plugs, with wall film removed. Although treatments 3 and 4 gavelarger average values in the case of the surviving seedlings,application of the T-statistical test used to compare treatmentsdemonstrated that these differences could not be classed assignificantly different. The T-test was insensitive because thepopulatiohs of surviving seedlings in the various treatments was small.In the case of the dead seedlings, the same statistical tests clearlyindicated that growth was signifidiscussed above. The effect of theflexible, perforated container wall or plug is also clearly indicated inthe decreased incidence of frost heaving in comparison to the rigid wallcontainer. This effect is attributed to the provision of greateropportunity of early root anchorage.

This example illustrates one suitable method for practicing theinvention. One bale of horticultural peat (6 cu ft., 104 lbs.) of 48percent moisture content was blended for 30 minutes with approximately189 lbs. of water in a 30 cu ft. paddle mixer which had a blade speed of20 rpm. The mixture, having a uniform moisture content of 81.45 percent,was discharged and transferred to the hopper of a custom-built extruder,in accordance with FIG. 7. The mixture was extruded through a screwauger of compression ratio 2:1, turning at 600 rpm, and through a l X 8inches outlet nozzle, into a 1 inch diameter tubular polythene film of 1mil thickness at the front end. Lengths of 15 20 feet of 15 percent orless. The cut sections were packed in trays (98 containers per' tray).Seed depressions (178 X 54inch) were made by a high-speed air-drivendrill and seeding of pine, spruce, or Douglas fir was conducted by a98-nozzle vacuum seeder. Tray design permitted stacking and palletizingoperations.

The seeded containers were transferred to a greenhouse whereillumination, misting, temperature and humidity control, irrigation andnutrient addition were carried out according to established "growthproce:

The lengths of filled container were cut into 3 inch sections using agang cutter equipped with 10 hollowground circular knives rotating at600 rpm and set at 3 inch spacings. Randomly-selected containers wereweighed in grams and their diameters and lengths measured incentimeters. The dry weight/wet volume density was 0.182g/cc with acoefficient of variation of dures, for periods up to 8 weeks, followedby at least an 8-week period outdoors to harden-off the seedlings.

Field planting consisted of selection of a desirable microsite,preferably on scarified soil, formation of a l X 3 inch holeeither byusing a dibble or a soil coring device. The thin plastic wall was eithermanually perforated or removed by slitting such that the plug of rootingmedium and the plant are inserted into the hole.

EXAMPLE [X This example further illustrates the improved survivability,growth and resistance to frost heaving of l8Week-old lodgepole pineseedlings field planted in extruded plugs as compared to field planted-l8-weekold seedlings grown in loose-fill hand-packed, rigid plastictubes of equal rooting volume. The site was a level field of rich TABLEVll Survival i970 seasons growth* Frost heaved Per Per- 7 Per- Per- Per-Per- No. Percent Percent No. cent cent cent cent cent cent Percent centcent counted survival mortality counted V4 86" 1" 1.5 2' 3 heaved alivedead Tifiriied container: PM

Lodgepole Pine... 50 94 6 0 3 White Spruce... 24 92 2| 3 2 Douglasfir 520 l Tubeling:

Lodgepole Pine:

Tube removed 87 6i 3) 54 4 56 28 7 5 29 7 l8 Tube intact 93 6i 3) 55 2747 20 5 96 53 36 White Spruce:

Tube removed 7) 63 37 43 19 29 l0 2 4 l9 8 7 Tube intact 77 5) 41 31 3527 4 2 90 41 28 V TABLE VIII (Survival and Growth of Lodgepole PineSeedlings) Loose fill Container: Compressed cylinder hand pack Density:0.142 0.187 0.206 0.110

Polythene Polythene Polythene skin slit or Encased in skin slit orEncased in skin slit or Encased in Rigid Wall treatment: removed rigidtube removed rigid tube removed rigid tube tube Series: 17 I8 19 20 '212'2 2'3 Noibiaind', July M0 .Jffifiil 5s 59 5s 29 28 1s Plantingmortality. Fall I970 5.7 8.5 9.0 10.2 17.2 3.6 27.8 Winter mortality.Spring l97l 3.7 5.6 4.3 NJ 0 3.7 23 Cumulative mortality. Spring I97!l%).. 9.4 [3.6 22.4 20.3 l7.2 7.! 44.4 Cumulative survival. Spring I97]90,6 86.4 77.6 79.7 82.8 92.) 55.6 Mean sccdling height (cmii' 7.8 6.28.0 6.2 8.6 8.5 4.0 Frost heaved 2 40 2 28 0 7 0 Average height ofheaved container (cm) 2.5 1.7 2.5 2.4 0 1.6 0

black loam, free of weeds and competitive vegetation. The 1 inchdiameter extruded containers were planted at 4 foot spacings with eitherthe polythene skin removed or slit longitudinally in at least four equalspac-- ings around the circumference. After the mid-summer planting, thesite received minimal rainfall for the remainder of the summer and fall;it received approximately 80 inches of snowfall during the winter. Anumber of treatments were tested to illustrate the effect of compressingthe peat into cylinders and also to test the effect of encasing therooting medium in a rigid wall, and also to compare densities of rootingmedium The control containers consisted of low density, loose fill,hand-packed comminuted peat loaded into 1 inch diameter rigid walltubes.

Table VI" clearly illustrates the superior survival and growthcharacteristics for seedlings grown in the compressed extruded plugs(Series 17, 18, 19, 20, 21 22), with or without a container wall, whencompared to those grown in the loose-fill media of equal volume (Series23). These effects are related to the peatmoisture relationshipsdiscussed above. The frost heaving effect which is aggravated by rigidwall container systems is clearly illustrated in the three pairs tested(Series 17-18, Series 19-20, Series 21-22).

EXAMPLE x w This example illustrates the use of peat-loam mixture togrow vegetables and flowers. Systems containing horticulture peat andrich black loam, by volume, were TABLE IX Peat Soil Feed AccpetablePlant Series (volzvol) Moisture Response at Wk.8 23 4 l 59 yes 24 4 1 l60 yes 25 4 l I 62 yes 26 9 l 66 yes 27 9 l 69 yes 28 9 l 73 yes 29 l9 l65 no 30 l9 l 69 no 3] l9 l 74 no blended and adjusted to the watercontents described in Table IX. Fifty containers of each series wereseeded to tomato, leaf lettuce, head lettuce, marigold and aster. Thecontainers were grown under a fluorescent lamp source of 800 ft-candlesand 16 hour photo period for 8 weeks. Satisfactory seedlings wereobtained in Series 23, 24, 25, 26, 27, 28. The acidic medium of Series29, 30, and 31 produced undersized plants.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A seedling container unit comprising:

a coherant, solid, extruded, cylindrical body consisting essentially ofcompressed, comminuted peat, having 'a Von Post decomposition rank ofabout 1-3, and water, provided in an amount between percent and percentby weight of the body at the time of extrusion, said body having flatends, the curved surface of said body being encased by a thin,impermeable, flexible, plastic film, the top and bottom end faces of thebody being unencased, said body further having a substantially uniformdry weight/wet volume density throughout its length and width, saiddensity being between about 0.13 gms/cc and 0.25 gms/cc, said bodyhaving a seed or seedling planted in a flat end face thereof.

2. A process for producing seedling container units useful for rearingseedlings comprising:

mixing loose peat with water in an amount between 70 percent and 85percent by weight of the mixture and in the absence of any binder toform an extrudable mixture;

compressing and comminuting the peat in the mixture by extruding themixture to form a continuous, coherant, cylindrical body of peat havinga uniform dry weight/wet volume density of between 0.13 gms/cc and 0.25gms/cc;

encasing the cylindrical body in a thin, flexible, im-

permeable casing; and

slicing the encased body transversely to its longitudinal axis to form aplurality of container units.

1. A seedling container unit comprising: a coherant, solid, extruded,cylindrical body consisting essentially of compressed, comminuted peat,having a Von Post decomposition rank of about 1-3, and water, providedin an amount between 70 percent and 85 percent by weight of the body atthe time of extrusion, said body having flat ends, the curved surface ofsaid body being encased by a thin, impermeable, flexible, plastic film,the top and bottom end faces of the body being unencased, said bodyfurther having a substantially uniform dry weight/wet volume densitythroughout its length and width, said density being between about 0.13gms/cc and 0.25 gms/cc, said body having a seed or seedling planted in aflat end face thereof.
 2. A process for producing seedling containerunits useful for rearing seedlings comprising: mixing loose peat withwater in an amount between 70 percent and 85 percent by weight of themixture and in the absence of any binder to form an extrudable mixture;compressing and comminuting the peat in the mixture by extruding themixture to form a continuous, coherant, cylindrical body of peat havinga uniform dry weight/wet volume density of between 0.13 gms/cc and 0.25gms/cc; encasing the cylindrical body in a thin, flexible, impermeablecasing; and slicing the encased body transversely to its longitudinalaxis to form a plurality of container units.